The Chemical Dissolution of Soda-Lime Silicate for Safe

The Chemical Dissolution of Soda-Lime Silicate for Safe DrinkingApplications

Sara Bendaoud Xining [email protected] [email protected]

Roshan Vasoya Megan [email protected] [email protected]

Jin [email protected]

Abstract:To create a more cost effective glass

while preserving its safety, the compositionof soda-lime silicate glass was modified.The amount of Silicon dioxide in thecomposition was decreased in order to lowerthe melting point of the glass, thus makingthe new glass more cost-effective due tolower energy consumption. Calcium oxideand sodium oxide concentrations wereincreased to raise chemical durability andlower the melting temperature respectively.The glass was crushed and poured into 500mL of each Pepsi Cola, Arizona Iced Tea,and tap water: three common beverages thatvary in pH. The glass composition was thenanalyzed through pH changes, Fourier-transform infrared spectrometry (FTIR), andmass loss. It was found that less than 10% ofglass mass was dissolved in each of the threebeverages. The pH values showed that theglass caused the beverages to turn basic,while the control groups turned acidic, withthe exception of tap water. FTIR analysisdemonstrated that the mass loss was mainlySilicon and oxygen. Thus, this compositionof soda-lime silicate glass composition is acost-efficient, alternative method toindustrial glass.

1. Introduction:

Soda-lime silicate glass is used forvarious purposes, most commonly in thepackaging industry. Since glass is used tostore items such as foods and liquids on adaily basis, it is imperative to ensure that theglass does not dissolve into the liquid that itcontains. The most effective container glassshould be safe for usage, but also relativelyaffordable. The objective of this researchproject is to create a unique glasscomposition that reacts minimally withbeverages, yet remains cost-effective.Economic feasibility is an important aspectto consider, as a safe drinking glass shouldbe priced well for consumers. Unfortunately,it is extremely impractical to account for allproperties of both glass and beverages thatmay affect dissolution rates of the former.Thus, the research project is centered on therelationship between pH of the liquid andglass dissolution.

There are multiple facets of theproduction process vital to the making of anideal glass, most importantly those thatrevolve around the heating of the glass.Creating a ceramic glass involves heatingparticular powdered substances together inspecific ratios at high temperatures toproduce a molten glass, then cooling it toprovide a finished product. In particular, thetemperature required to heat a manufactured

glass today is 1675°C. However, bychanging the composition of a glass, it ispossible to lower the melting point, yieldinga glass that requires less energy, and thusless money, to produce.

The soda-lime silicate glasscomposition differs from the standardcomposition in that it contains less Silicondioxide. Silicon dioxide has a high meltingpoint of 1610° C due to the strong Silicon-oxygen covalent bonds that must be brokenthroughout the glass.1 By decreasing theamount of Silicon dioxide, less energy isexpended to create the glass.

Table 1 compares the difference incomposition of the regularly produced soda-lime silicate glass today with thecomposition of the modified glass used forthis experiment. There is a change in relativecomposition seen for most of thecomponents, with a decrease in Silicondioxide and an increase in all of the otherpowders. Boron oxide was not present in theindustrial standard composition, so therewas no calculated percent change seen.

2. Background:

2.1 Chemical Composition of Soda-limeSilicate Glass

Soda-lime silicate glass is a commontype of glass, used commercially to preparewindowpanes and containers such as bottlesand jars. Various forms of this glass exist,each with a unique chemical composition. Inorder to create glasses with differentproperties, it is possible to change the typesof compounds used as well as the ratiosbetween these compounds.

The foremost component ofindustrial glass is Silicon dioxide (SiO2),supplemented with glass modifiers likeCalcium oxide (CaO), and sodium oxide(Na2O). Other common compounds in theglass include aluminum oxide (Al2O3) andmagnesium oxide (MgO). The glass used in

this project is different in that it containsboron oxide (B2O3), which soda-lime silicateglass does not normally contain. Boronoxide was added because it resists water andacids.2 Also, percentages of typical glasscomponents were moderately changed.

The various materials in a glassmixture all play vital roles in the overallproperties of the glass. The properties of aspecific compound can alter those of anotherwhen placed in the same batch. In order toreduce the melting point of a silicate glass,sodium oxide, with a melting point of920°C, is added to the mixture.3 However,by adding sodium oxide, the glass thenbecomes more soluble in water. In order tocounteract this negative effect, Calciumoxide is added to the mixture, as it makesthe glass more insoluble again.4

Temperature and energy are relatedwith the following formula:

(3/2)kT = kinetic energy, with kbeing a constant.5 This formula demonstratesthat temperature and kinetic energy aredirectly proportional thus, the higher themelting temperature, the more kineticenergy that is required in the meltingprocess. Thus, by decreasing the meltingpoint of the glass, energy is saved.

2.3 CalcinationCertain materials, such as Calcium

oxide, sodium oxide, and boron oxide arenecessary components of soda-lime silicateglass. However, in order to ensure costefficiency, Calcium carbonate, sodiumcarbonate, and boric acid are oftenpurchased in lieu of the former materials.Calcination is then used to convert thecheaper materials into the desired ones.Calcination is the decomposition process inwhich chemical substances are heated totemperatures between 800-1000° C in orderto remove volatile substances, water, andother impurities from the material.6

Different chemicals have distinct calcinationtemperatures. For example, the calcination

temperature of Calcium carbonate is 850°C.7 This is important to consider whendetermining the process of calcination andmelting.

2.2 Annealing and QuenchingGlass is an amorphous structure in

which atoms are randomly arranged asopposed to a crystalline structure whereatoms follow a specific pattern. Thus, acrystal and glass can have the samecomposition, yet differ in internalarrangement, as seen with silica glass andquartz, both SiO2.

Whether a melted substance becomesa crystal or glass depends upon the methodof cooling. In order to make glass, themelted batch must be cooled very quickly toensure that the atoms do not have time toform an ordered structure. An amorphousstructure can be molded into any shape,whereas crystalline structures harden into aninvariable structure. Therefore, anamorphous structure is ideal for formingcontainers suitable for this particularexperiment. The process of rapid cooling isreferred to as quenching.

Quenching can be accomplished inmultiple ways, such as by using air, water,and metal. The rapid cooling results instresses within the glass that may cause it tobreak very easily.8 Thus, the glass must beannealed after the quenching process.Annealing is the process in which a glass isslowly cooled at a constant rate through aspecific temperature range.9 Soda-limesilicate glass has an annealing point of 546°C. This is the temperature at which theinternal stresses, like tensile andcompressive stresses, are relieved withinthe glass.10

2.4 Dissolution of Glass in VaryingBeverages

In order to test the chemicaldurability of the glass, the experiment willconsist of placing the crushed pieces of glass

into three different common beverages withvarying pH levels. The drinks will rangefrom very acidic to neutral: Pepsi Cola, withan initial pH of 2.55; Arizona Iced Tea, witha pH of 2.85; and tap water, with a pH of7.07.

These three beverages will be testedfor any changes in pH levels that will resultfrom exposure to the glass. If the pHchanges significantly, the glass is not asdurable and as safe as hoped for. Thebeverages will have a control group to becompared with and to take intoconsideration of any natural changes in thepH of each beverage.

Dissolution is the separation intocomponents of a certain material. In ourexperiment this material is glass. Thedissolution of the glass would imply its lackof durability, thus, making the glassinappropriate for drinking applications.Observing the amount of dissolution of theglass is another method of testing thedurability and safety of the container glass.The dissolution of the glass can be tested bytwo different methods: FTIR and mass loss.

2.5 FTIRFTIR stands for Fourier-transform

infrared Spectroscopy, which is tested with aspectrometer. This is used to identify amaterial based on the bonds of which it iscomposed, and it can also measure theamount of material that exists in a sample.11

The graph that is produced from thisprocess, which is Figure 8, can be read bylooking at the valleys in the spectrum.Certain peaks represent specific bonds. Ifthere are higher peaks, there contains moreof that identified bond. The lower thetransmittance, the more of the correspondingbond it contains.12

FTIR is also especially useful due toits abilities to find the infrared frequenciesof the material it is testing. Because eachindividual compound absorbs uniqueinfrared frequencies based on which bonds

are present, finding the infrared frequenciesof a compound can identify the material andbonds that it is made up of.11 This methodcan be used in order to identify the certainbonds that consist of the glass before andafter its exposure to the various pH levels.This can identify how the glass was affectedinternally and chemically as a result of theexposure to the different environments.

The FTIR spectrometer has aprocedure that has been refined over time.Generally, the spectrometer projects aninfrared light that detects which wavelengthsare present in the compound. Each bond hasa unique bonding energy, thus allowing theFTIR to identify bonds based off theinfrared frequencies that it either absorbs orreflects back. Therefore, FTIR is veryconvenient when identifying theconcentration of the bonds as well as theatoms involved in it.

Another way to identify thedurability of the glass is by measuring themass loss of the glass. As a result of theexposure of the glass in various pHenvironments, there is expected to be massloss. Mass loss is the amount of glass thatwas dissolved into the drink. The smaller theamount of mass loss, the less that the glassdissolved into the beverage, which meansthe glass is more durable.

Overall, there are three ways that theglass’s durability will be tested: pH change,FTIR, and mass loss. These methods willgive information on the chemical structureof the glass before and after the exposure, aswell as the physical effects that occurred. Byusing the various techniques to see theamount of glass that dissolves into thedrinks, the overall safety of this cost-effective, modified glass can be determined.

3. Experimental Approach:

3.1 Materials:1. Mortar/pestle2. Silica crucible3. Platinum crucible4. Annealing furnace5. Silicon Dioxide (SiO2)6. Sodium Carbonate (Na2CO3)7. Calcium Carbonate (CaCO3)8. Aluminum Oxide (Al2O3)9. Boric Acid (H3BO3)10. Pepsi-cola11. Tap water12. Arizona Iced Tea13. Acetone (C3H6O)14. Scale15. Aluminum foil16. Metal slab17. Syringe18. Filter paper19. Funnel20. Bottles

3.2 Determining the Glass Composition:First, calculations were made based

on what was necessary to make the desiredbatch. In the batch calculations, molarpercentages of the five compounds neededwere converted into mass percentages. Afterfinding the mass percentages, thepercentages by the mass of the glass weremultiplied to find the mass of each of thecompounds needed in the batch. Thencalcination conversions were made, fromNa2O to Na2CO3, CaO to CaCO3, and B2O3

to H3BO3. This was done by converting themass of the oxides to their moles. Then, themoles of the oxides were converted to molesof the compounds that were later calcined totheir mass.

After having the mass of each of thebatch compounds, measurements were takenout from the stock: 53.2 grams of SiO2, 5.47grams of H3BO3, 31.28 grams of Na2CO3,22.16 grams CaCO3, and 3.01 grams of

Al2O3. A balance and aluminum foil boatswere used to measure the masses of eachcomponent.

3.3 Creating Glass:To create the glass, the mixture,

except the Calcium carbonate component,was continuously stirred for approximatelythirty minutes, using a mortar and pestle.Then, the Calcium carbonate wasindividually calcined for 24 hours, reachinga final temperature of about 850°C beforebeing added to the batch. Subsequently, thecombined mixture was melted in a hightemperature furnace, formally known as theCarbolite BLF 1700, to 1650°C. Themixture was heated incrementally to1000°C, initially at a rate of 10°C/minute,but then 5°C/minute until the glasstemperature rose to 1650°C. Meanwhile,Na2CO3 and H3BO3 were calcined within thecrucible during the melt.

The molten glass was then taken outof the Carbolite BLF 1700, and quenchedupon a metal slab to an estimated 600°C.The glass was placed in an annealingfurnace, set at 525°C, in order to bring thetemperature down gradually over the courseof an hour, preventing the glass fromdeveloping cracks under its own pressuredue to the significant temperature change.

3.4 Creating Glass Powder:In order to perform the chemical

dissolution procedure, the glass was reducedto grains, ranging from 300 to 425micrometers. Grinding the glass within amortar and pestle increased the surface areaof the glass, promoting chemical reactionsbetween the glass pieces and the liquids at afaster rate. Due to a one-week time restraint,the glass was crushed in order to expeditethe rate of dissolution.

3.5 Chemical Dissolution:To complete the chemical dissolution

aspect, the chosen liquids had to be

measured and poured into 500 mLcontainers. Two 500 mL samples of IcedTea, Pepsi, and tap water each were poured.Then, 2 grams of glass, 300-425 microns indiameter, was put into one of each sample.The second acted as a control for eachbeverage. After the 138 hours passed and thefiltered samples dried, the masses of thesamples were determined and compared tothe original two grams to determine howmuch mass was dissolved within thebeverage. These samples were then used inthe FTIR to determine what specific bondswere lost within the beverages.

3.6 pH Readings:In this case, the grinded glass was

placed into various common beverages inorder to determine the degree of dissolution.Also, pH measurements were periodicallyrecorded in order to track pH changescaused by the glass. This process involvedutilizing a pH sensing device, officiallyknown as the Mettler Toledo SevencompactpH meter. The pH was measured over thecourse of 138 hours. During this process, apH probe was placed in each sample at arecorded time, and the measurement takenand recorded. After the sample was done,the pH probe was removed and rinsed in tapwater. It was then returned to the probehousing and used for the next beverage.

3.7 Filtration:First, a funnel with filter paper was

set up over a beaker to remove the excessliquid in the container with the glass. Toremove the bulk of the liquid, a largesyringe was used to ensure that no glass waslost. The filter paper further ensured thatglass was not accidentally removed. Whenonly a small amount of each beverageremained, the containers were put in an ovenat 50°C to remove the last traces of liquidfrom the glass. In the cases of Pepsi-colaand Arizona Iced Tea, the liquids werewashed out with tap water to ensure that

when the liquid evaporated in the oven, thesample wasn’t contaminated with sugar orother particulates.

3.8 Mass Loss:The empty bottles were massed

along with dry filter paper containing thefiltered glass. These mass measurementswere compared to the original mass of thefilter paper after being placed in the samedehydrating environment and the originalmass of each bottle.

3.9 FTIR:After finding the mass lost in each

sample, the glass in each was taken for FTIRanalysis. This was done by placing thesample in front of the IR source and runningthe FTIR. Figure 8 was then retrieved andanalyzed to determine the bonds. Deviationsin the peaks of the graph show differences inthe bonds that were still within the glass.SiO2 bonds are in the 1000-1280 cm-1

range13, Na-O bonds are in the 538 cm-1

range 14, Ca-O bonds are represented at the665 cm-1 valley (previous source), Al-Obonds are at the 935 cm-1 valley, and B-Obonds are at the 720 cm-1 valley.15

4. Results and Discussion:

4.1 pH Change:A safe drinking glass contains

elements that minimally alter the pH of theliquid within the glass. Table 2 shows thepH readings of the three liquids, tap water,Pepsi Cola, and Arizona Iced Tea. Therewere a total of 5 readings per liquid, andeach time that the pH reading was taken wasrecorded with the time and date. Table 3shows the pH readings of control liquids.

As seen in Tables 2 and 3, there is amore alkaline trend for all of the drinks.This means that the glass caused all of thebeverages to turn more basic, although thepH values only changed within 0.10. Themost significant change was observed in the

tap water.For tap water, there was more of a

pH change in the control than that of theexperimental, although both groups turnedmore basic. However, for the pH changes ofthe control groups of the Pepsi and ArizonaIced Tea, they turned acidic, as compared tothe increase in pH of the experimentalgroups. Due to the pH buffer that is presentin Pepsi Cola, fumaric acid, 16 it is possiblethat the data values received on the Pepsicola are an underestimate. This is becausebuffers resist pH changes in beverages.

The pH change was deemedinsignificant because it varied within a fewtenths of a unit, which does not drasticallychange the acidity of a liquid.

4.2 Mass Loss:Initially, 2.0 grams of soda-lime

silicate glass were poured into 500.0 mL ofPepsi Cola, Arizona Iced Tea, and tap water.After 138 hours, the amount of glass left inthe bottles was measured to determine theamount of glass that dissolved in the variousbeverages. A significant change in masswould indicate that the glass is unsafe forcommercial application as it would leach, ordissolve, into the contained beverages. Onthe other hand, a small change in masswould indicate that the glass is safe. As seenin Figure 7, it was determined that the leastamount of glass was dissolved in tap water,with only a 4.0% decrease in glass mass.There was a 4.5% decrease in mass of glasspoured in iced tea. The most significantchange in mass occurred in the Pepsi-colabottle, with a 6.5% decrease. The variouspercent changes demonstrate that glassleaching is not only dependent upon glasscomposition, but also upon the type ofbeverage held in the glass container. 17

While determining if there wassignificant mass loss, it was found that themass loss for all three beverages was lessthan 10%. In other words, the mass loss isnegligible. Also, it important to note that the

surface area to volume ratio for the glass andbeverage respectively was very high becausethe glass was crushed. In a fine powderedstate, the glass is more likely to react withthe liquid. In industry, the glass is shapedinto a container, in which the surface area tovolume ratio will be significantly lower.Thus, it is expected that the mass of glassleached into the beverage would be evenlower due to less reactions between glassand liquid.

4.3 FTIR:The results of the FTIR display the

two key aspects of the experiment: whichglass sample dissolved the most in itsenvironment; and which component of theglass dissolved the most. Of the threebeverages Arizona Iced Tea, Pepsi, and tapwater, the glass submerged in Arizona IcedTea leached into the beverage the least,followed by tap water and Pepsi. This wasseen by the order, going up the graph, thatthe lines were in, which can be seen inFigure 8. The leaching into the tap water,which had the second-to-least amount, wasmost likely due to the lack of a presence of abuffer or chemicals, unlike the Pepsi and theArizona Iced Tea, respectively. The particlesof Pepsi, an acidic carbonated beverage,were constantly moving and therefore hadmore collisions with the glass. This madethe dissolution more noticeable than ineither other beverage.

Of the glass that was dissolved, therewere certain chemicals of the batch thatleached more than others. As seen in thedifferences in the space between the peaks,it was seen that some compounds leachedinto their beverages more than others, whichcan be seen in Figure 9. SiO2 leached themost along with Al2O3. Both act as glassformers, therefore the structure of the glassitself dissolved into the beverages. Toclarify, Al2O3 is an intermediate, not aformer, which means it acts as both a glassmodifier and a glass former. Though this

seems detrimental to the durability of theglass, it is important to remember the massloss indicated that an insignificant amount ofglass dissolved within the beverages. Theother components, except for Sodium andOxygen bonds, were followed a typicaldissolution pattern. And with little variationbetween Boron and Calcium to Oxygenbonds, it can be deduced that they did notdissolve to an alarming magnitude.

Throughout this experiment, possiblesources of error exist. Firstly, the pH bufferpresent in Pepsi could have caused a slowerchange in the pH values for Pepsi. Inaddition, FTIR can only analyze a certainrange of wavelengths. For example,Sodium-Oxygen bonds were not able to bedetected. Another source of error may havebeen from some moisture present in thefilter paper and container even afterevaporation, causing differences in the massloss calculations. There were no otherknown sources of error besides human error.

5. Conclusions:The soda-lime silicate glass, created

as a modification of the industrial standardglass composition, is a cost-efficientalternative to the commonly produced glass.Although the glass was placed into threedistinct beverages with varying pH values,the pH values of all three beverages becamemore basic over the course of 138 hours.Furthermore, mass loss was calculated under10% for all three of the beverages. Finally,as seen in the FTIR, most of the mass loss,which was negligible, was probably due tothe Silicon dioxide bonds, and the mostmass loss was confirmed to have occurredwith the Pepsi.

Dependent on the values ofsignificance used in this particularexperiment, the mass loss under 10%, theminor changes in pH, and the results fromthe FTIR, the modified soda-lime silicateglass is a potential alternative towards a

more cost-efficient, safe drinking glass. As itrequires less energy to create due to thedifference in composition of the powdersthat it is made out of, it requires less moneyto produce, which makes a significantimpact in mass production.

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Infrared Spectrometry, 1st ed.(Thermo Nicolet Corporation,Madison, n.d.), pp. 1-7.

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Appendix

Table 1: Composition of Industrial Standard Soda-Lime Silicate Glass vs. Modified Glass

Table 2: pH Readings of Beverages with Glass

Table 3: pH Readings of Control Beverages

Figure 1: Soda-Lime Silicate Glass, after breaking

Figure 2: Weighing boat & Scale





Figure 3: Labeled 500 mL bottles

Figure 4: pH reading of Iced Tea

Figure 5: pH Reading of Pepsi Cola

Figure 6: pH Reading of Tap Water

Figure 7: Glass Mass Change Due to Dissolution in Various Beverages

Figure 8: Fourier-Transform Infrared Data

Figure 9: Labeled Relevant FTIR Section







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The Chemical Dissolution of Soda-Lime Silicate for Safe